Do you see an old woman or a girl?
I saw in the FB an illusion about which you probably heard, but I saw it for the first time. The picture is called "My wife and my mother-in-law." Its author placed the image of both in one picture - and the viewer sees only one of them. Someone's wife, and someone's mother-in-law.
I didn’t see how much I couldn’t see someone else here besides the old woman. Strange how so! But it turns out that American scientists interviewed a bunch of people in order to identify patterns. Why someone sees only the old woman, and someone only the girl (in the sense immediately, on the move without prompting and long peering).
So, the pattern is this ...
It turns out that those who are under 30 see a girl. And after 30 - her mother.